PDPs have been becoming widespread as large-screen display devices for television and computer output since color display was practically realized on the PDPs. Now the market demands larger screen devices with higher definition.
Among the PDPs, surface discharge-type AC-driven PDPs are commercialized. The surface discharge type is a type in which first and second main electrodes which act alternately as positive electrodes and negative electrodes in AC driving utilizing wall charges for sustaining a lighting state are arranged in parallel in one of a pair of substrates. Since the main electrodes extend in the same direction, third electrodes crossing the main electrodes are required for selecting cells. The third electrodes are placed on the other one of the pair of substrates to be opposed to the main electrodes with intervention of a discharge gas space in order that electrostatic capacity of the cells is reduced. When a picture is displayed, addressing is carried out for controlling wall charges according to the contents to be displayed, by generating address discharge across one of each main electrode pair (e.g., the second electrode) and the third electrode. After addressing is performed line by line, for example, alternating voltage for sustaining lighting is applied to the main electrode pairs at a common timing to all rows to generate surface discharge along the surface of the substrate only in cells having wall charges. When the cycle of applying the voltage is shortened, it is possible to obtain a seemingly continuous lighting state.
In a surface discharge-type PDP, it is possible to suppress deterioration of fluorescent layers for color display owing to ion impact during discharge and extend the life of the PDP by providing the fluorescent layers on the other substrate opposed to the substrate on which the main electrode pairs are disposed. PDPs having the fluorescent layers on their rear substrates are referred to as “reflection type PDPs” and PDPs having the fluorescent layers on their front substrates are referred to as “transmission type PDPs.” The reflection type PDPs, in which light is emitted from front side surfaces of the fluorescent layers, are superior in luminous efficiency.
In a commercialized reflection type PDP, address electrodes are placed as the third electrodes on the rear substrate. The address electrodes are covered with a dielectric layer, on which barrier ribs are formed to partition a discharge space by the column. The fluorescent layers are provided to cover sidewalls of the barrier ribs and exposed faces of the dielectric layer. The formation of the barrier ribs only on one substrate facilitates alignment in assembly of the pair of substrates. The provision of the fluorescent layers even in the sidewalls of the barrier ribs enlarges a light-emitting area and widens a viewing angle. The dielectric layer functions as a dielectric for providing electrical characteristics suitable for driving. In addition, in the case where the barrier ribs are formed by sandblasting, the dielectric layer is used as a cutting-resistant layer to prevent over-cutting in a depth direction and protect the address electrodes.
Conventionally, a PbO— or ZnO-containing low-melting-point glass, the thermal expansion coefficient of which is only a little different from that of the substrate, is used as a material for the dielectric layer covering the address electrodes. This low-melting-point glass as a base is mixed with a filler having a refractive index greatly different from that of the base, such as titanium dioxide (TiO2: titania), for the purpose of whitening the dielectric layer. The dielectric layer, if whitened, can reflect light that is emitted from the fluorescent layers and travels toward the rear substrate, to the front substrate, thereby enhancing the luminance. A white dielectric layer has a larger reflectance with regard to visible light than a transparent one.
With conventional PDPs, there is a problem in that a large amount of electric power is consumed wastefully in charging and discharging of a floating capacity between address electrodes. As the size of cells is reduced for higher definition, the floating capacity becomes larger. Consequently reactive power increases and also the waveform of a driving pulse turns dull, which result in a remarkable delay in response during driving. As the number of pixels is increased, more power is required for addressing. Therefore, the floating capacity has more serious effect from the viewpoint of heat generation. For example, as compared with a VGA specification (640×480 pixels) for NTSC television system, a SXGA specification (1280×1024 pixels) has more than twice as many rows and twice as many columns as the VGA specification. Accordingly, in order to ensure a normal frame rate, the frequency of a pulse applied to the address electrodes must be doubled at least. In addition to that, the number of address electrodes is doubled. Consequently, addressing requires four times more electric power.
There is another problem in that specific sites on an inside face cannot be sufficiently whitened for enhancing the luminous efficiency. That is, if the content of the filler for whitening is increased as a first technique, the dielectric constant of the dielectric layer increases and more power is consumed. That is because the relative dielectric constant of the filler (e.g., 80 to 110 for titania) is extremely larger than that of the lower-melting glass base (10 to 14). If the dielectric layer is thickened as a second technique, the lower limit of drive voltage in addressing rises. Also in order to ensure a discharge space having a desired volume, the thickness of the dielectric layer provided as a reflective layer is required to be as small as possible.
An object of the present invention is to increase the luminous efficiency. Another object of the present invention is to provide a plasma display panel having a dielectric layer whose relative dielectric constant is small and whose reflectance is large.